This invention relates to an improved preservative system for ophthalmic solutions, especially solutions for the care of contact lenses. The solutions contain as the preservative chlorhexidine and polyhexamethylene biguanide, or salts thereof.
Since ophthalmic solutions, including solutions used for the care of contact lenses, either directly or indirectly come into contact with the eye, it is important that the solutions do not become contaminated with microorganisms. Conventionally, such solutions are packaged under sterile conditions, and many solutions incorporate an antimicrobial agent as a preservative for inhibiting growth of microorganisms which may contaminate the solution. For ophthalmic solutions used for contact lens care, the antimicrobial agent often also serves to disinfect and/or preserve contact lenses when rinsed or immersed in the solution.
A challenge is to develop preservative systems which not only have a wide spectrum of antimicrobial activity but which also are more suitable for ophthalmic applications and less irritating to the eye. Preservatives provide desired antibacterial effects, but preservatives are, by their nature, irritating to the eye. Thus, while antimicrobial efficacy of a solution could be improved by merely increasing the amount of the active agent, the potential for eye irritation increases as the concentration of the active agent is increased. Conversely, decreasing the concentration of the antimicrobial agent could lessen eye irritation, but antimicrobial efficacy would decrease.